1. Field of the Present Invention
This invention relates to filters for separating leukocytes, leukocyte removers, filters for separating both leukocytes and platelets, and leukocyte/platelet removers, and more particularly to those having excellent capability of capturing leukocytes without suffering from contamination with foreign matters.
2. Prior Art
In recent years, the form of blood transfusion has been changed from conventional whole blood transfusion to blood component transfusion by which only a necessary component is transfused to a patient. The important point of the blood component transfusion is how to increase the purity of respective blood components fractionated.
Blood from donors has conventionally been centrifugally separated into concentrated red cells (CRC), a platelet concentrate (PC), and a platelet-poor plasma (PPP). Blood preparations obtained by the separation of blood are used for blood component transfusion to patients who need red cells or platelets. However, since a large amount of leukocytes are contained in blood preparations, problems may sometimes take place by injecting a large amount of leukocytes into patients by transfusion.
Leukocytes contained in blood preparations must be removed to the possible extent for the purpose of avoiding side effects, namely post-transfusion reactions. To date, a number of improvements have been proposed for this purpose. In some cases, extraction of red cells alone by excluding leukocytes and platelets is also required. Used for these purposes are a method using a capturing member, a gravitational centrifugal separation method utilizing the difference in specific gravity between blood cells, a method utilizing the viscidity or adhesion of leukocytes, etc.
Among them, the method using a capturing member is widely used because of good efficiency in removing leukocytes or leukocytes and platelets, easiness of handling, etc. Capture members often used are fibers having extremely small diameters such as natural fibers, synthetic fibers, etc. packed into a column, or non-woven fabrics formed by secondary-processing them.
The use of such fibers, however, is likely to suffer from detachment of some fibers or outflow of foreign matters during operation. If the fiber packing density is increased for the purpose of sufficiently capturing leukocytes or platelets, trapped blood cells tend to clog pores between the fibers.
On the other hand, there are various proposals to use porous members as the capturing members. For example, Japanese Patent Publication No. 61-39060 discloses the use of a porous member including continuous fine pores with an average pore diameter of 25 .mu.m to 60 .mu.m to capture highly viscous monocytes and granulocytes. Japanese Patent Publication No. 63-26089 discloses a method using a porous member having continuous pores with an average pore diameter of 5 .mu.m to 20 .mu.m to capture leukocytes by utilizing the viscidity of white cells and by filtration with the fine pores of the porous members.
However, in view of the recent demand for more effective removal of leukocytes, the above porous members having relatively large pore diameters do not provide satisfactory leukocyte separation. Leukocyte-separating abilities are elevated by reducing the pore diameter (for example, by reducing the average pore diameter to less than 3 .mu.m or so); however, blood cells trapped are likely to clog the pores of the porous members, taking much time for filtration.
Thus, there have so far been no leukocyte filters, leukocyte/platelet-separating filters, and removers comprising such filters with sufficient performance for the practical purpose, and their improvements are still desired.